20181245 Ver 2_O and M Bioretention Area_20200817

2020
Stormwater operation
and maintenance
manual
FERGUSON STREET DEVELOPMENT
WILLIAM STILLWELL
Maintenance

Bioretention maintenance requirements are typical landscape care procedures and include:

A. Watering: Plants should be selected to be tolerant of the bioretention facility’s particular
conditions. Watering may be required to initially establish the vegetation. Watering should not
be required after establishment (about 2 to 3 years). However, watering may be required during
prolonged dry periods after plants are established.
B. Erosion Control: Inspect flow entrances, ponding area, and surface overflow areas
periodically. Replace soil, plant material, and/or mulch in areas where erosion has occurred.
Erosion problems should not occur with proper design except during extreme weather events. If
erosion problems do occur, the following issues should be re-assessed: flow volumes from the
contributing drainage area and bioretention size; flow velocities and gradients within the
bioretention facility; flow dissipation and erosion protection methods in the pretreatment and in-
flow areas. If sediment is deposited in the bioretention facility, immediately determine the
source, remove excess deposits, and correct the problem.
C. Plant Material: Depending on plants selected and aesthetic requirements, occasional
pruning and removal of dead plant material may be necessary. Be careful to prune trees and
shrubs to maintain lines of sight in parking lots and along roadways. NCDOT states: “Shrubs
must be kept low, and trees and large shrubs under-trimmed sufficiently to permit clear sight in
the area between 2 feet and 6 feet above roadway elevations. Replace all dead plants.
However, if specific plants consistently have a high mortality rate, assess the cause and replace
with appropriate species. Periodic weeding is necessary until groundcover plants are
established. Weeding should become less frequent if an appropriate plant density has been
established.
D. Nutrients and Pesticides: The soil media and plant material should have been selected
for optimum fertility, plant establishment, and growth within the particular conditions of each
bioretention facility. Nutrient and pesticide inputs should NOT be required and will degrade the
pollutant processing capability of the bioretention facility, as well as contribute to additional
pollutant loading to receiving waters. By design, bioretention facilities are typically specified in
watersheds where phosphorous and nitrogen levels are often elevated. Therefore, these should
not be limiting nutrients with regard to plant health. If in question, have the soil analyzed for
fertility. Addition of commercial fertilizer or compost to bioretention will likely result in nutrient
export from the bed.
E. Mulch: Replace mulch annually in bioretention facilities where heavy metal deposition is
likely (e.g., drainage areas that include commercial/industrial uses, parking lots, or roads). Metal
‘hot spots’ occur where water enters the bed. In residential or other settings where metal
deposition is not a concern, replace or add mulch as needed to maintain a 2 to 4-inch depth.
F. Filtering Capacity: When the filtering capacity diminishes substantially (e.g., when
water ponds on the surface for more than 12 hours), remedial actions must be taken. If the
water still ponds for more than 12 hours, the top few inches of material should be removed and
replaced with fresh material. The removed sediments should be disposed of in an acceptable
manner (e.g., landfill) or land application. If that does not solve the problem, more extensive
rebuilding is required. If the bed has filter fabric installed under the media and above the
washed rock, the filter fabric may be clogged with sediment. If clogged filter fabric is present, the
bed will need to be rebuilt.

When to Perform Maintenance:

A. Replace gravel when it has
become clogged with sediment.

B. Replace mulch when it becomes
thin or is taken over by grass.
Manually or mechanically remove
grass – do not spray herbicide.

Operation and Maintenance Provisions
A. Immediately after the bioretention cell is established, the plants will be watered twice
weekly if needed until the plants become established (commonly six weeks).
B. Snow, mulch or any other material will NEVER be piled on the surface of the bioretention
cell.
C. Heavy equipment will NEVER be driven over the bioretention cell.
D. Special care will be taken to prevent sediment from entering the bioretention cell.
E. Once a year, a soil test of the soil media will be conducted.
F. After the bioretention cell is established, Inspect it once a quarter. Records of operation
and maintenance will be kept in a known set location and will be available upon request.
G. Inspection activities shall be performed as follows. Any problems that are found shall be
repaired immediately.
H. Remove top layer of fill media when the pool does not drain quickly. Based on the media
specification, the pool should drain within 24 hours.

Operation and Maintenance Provisions for Bioretention Cell

SCM element: Potential problems: How to remediate the
problem:
The entire bioretention cell Trash/debris is present. Remove the trash/debris.
The perimeter of the
bioretention cell
Areas of bare soil and/or
erosive gullies have formed.
Regrade the soil if necessary to
remove the gully, and then
plant a ground cover and water
until it is established. Provide
lime and a one-time fertilizer
application.
The inlet Blocking/Clogging? Unclog the pipe. Dispose of the
sediment off-site.
The pipe is cracked or otherwise
damaged (if applicable).
Replace or repair the pipe.
Erosion is occurring in the swale
(if applicable).
Regrade the swale if necessary
and provide erosion control
devices such as reinforced turf
matting or riprap to avoid
future problems with erosion.
Stone verge is clogged or
covered in sediment (if
applicable).
Remove sediment and clogged
stone and replace with clean
stone.
The pretreatment system
Flow is bypassing pretreatment
area and/or gullies have
formed.
Regrade if necessary to route all
flow to the pretreatment area.
Restabilize the area after
grading.
Sediment has accumulated to a
depth greater than three
inches.
Search for the source of the
sediment and remedy the
problem if possible. Remove the
sediment and restabilize the
pretreatment area.
Erosion has occurred. Provide additional erosion
protection such as reinforced
turf matting or riprap if needed
to prevent future erosion
problems.
Weeds are present. Remove the weeds, preferably
by hand.
Plant material
Best professional practices
show that pruning is needed to
maintain optimal plant health.
Prune according to best
professional practices Maintain
lines of sight between 2’-6’.
Plants are dead, diseased or
dying.
Determine the source of the
problem: soils, hydrology,
disease, etc. Remedy the
problem and replace plants.
Provide a one-time fertilizer or
lime application to establish the
ground cover if a soil test
indicates it is necessary.
Weeds are present. Remove the weeds, preferably
by hand. If an herbicide is used,
wipe it on the plants rather than
spraying.
Bioretention cell vegetation
Best professional practices
show that pruning is needed to
maintain optimal plant health.
Prune according to best
professional practices. Maintain
lines of sight
Plants are dead, diseased or
dying.
Determine the source of the
problem: soils, hydrology,
disease, etc. Remedy the
problem and replace plants.
Provide a one-time fertilizer
application to establish the
ground cover if a soil test
indicates it is necessary. If sod
was used, check to see that it
was not grown on clay or
impermeable soils. Replace sod
if necessary.
Tree stakes/wires are present
six months after planting.
Remove tree stake/wires (which
can kill the tree if not removed).
Bioretention cell mulch and
media
Mulch is breaking down or has
floated away.
Spot mulch if there are only
random void areas. Replace
whole mulch layer if necessary.
Remove the remaining much
and replace with triple
shredded hard wood mulch at a
maximum depth of four inches.
Soils and/or mulch are clogged
with sediment.
Determine the extent of the
clogging - remove and replace
either just the top layers or the
entire media as needed.
Dispose of the spoil in an
appropriate off-site location.
Use triple shredded hard wood
mulch at a maximum depth of
four inches. Search for the
source of the sediment and
remedy the problem if possible.
An annual soil test shows that
pH has dropped or heavy metals
have accumulated in the soil
media.
Dolomitic lime shall be applied
as recommended per the soil
test and toxic soils shall be
removed, disposed of properly
and replaced with new planting
media.
The underdrain, filter fabric
element, and outlet system
Clogging has occurred. Wash out the underdrain
system.
Clogging has occurred. Clean out the drop inlet.
Dispose of the sediment off-
site.
The drop inlet is damaged Repair or replace the drop inlet.
The receiving water Erosion or other signs of
damage have occurred at the
outlet.
Contact the NC Division of
Water Resources.